Our site has set up links to the current (i86 platform) version of PI over ethernet. Prior to that we ran serial links over serial to an older version of PI running on a VAX platform. At a physical level you can almost certainly set up a connection using a PCI card. The format of the data stream may take a little more effort to set up.
I had limited involvement in this job so sorry if the details are a little thin - we used an external consultant to help us with the migration from the VAX-based which they had maintained up to that point.
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If we learn from our mistakes I'm getting a great education!